Transit of Venus — last this century
On 6 June 2012 Venus crossed the face of the Sun as a small black dot for 6 hours 40 minutes. The next transit of Venus is in December 2117, so for most people alive today this was the last chance to see one.
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Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On 6 June 2012 Venus passed in front of the Sun. When a planet crosses the Sun's disk like this, the event is called a transit. This one began at 22:09 UT on 5 June and ended at 04:49 UT on 6 June, lasting 6 hours 40 minutes. From north-east Asia, eastern Australia and New Zealand the whole transit could be followed in daylight.
Venus looked like a round black dot printed on the Sun. Its apparent size was about one thirtieth of the Sun's diameter, so with a proper solar filter it could be seen without a telescope. Looking straight at the Sun with bare eyes or ordinary sunglasses badly damages the eyes, however, so people used solar-filter glasses or projected the Sun's image onto a screen.
The transit also mattered to scientists. At the time the Kepler space telescope, launched in 2009, was finding exoplanets by the dimming they cause when they pass in front of their stars. So astronomers studied sunlight that had passed through the atmosphere of Venus, as a practice run inside the solar system for reading the atmospheres of distant planets. The Hubble Space Telescope used sunlight reflected by the Moon as a mirror, and the Solar Dynamics Observatory (SDO) recorded the whole crossing from space in sharp detail.
The next transit of Venus is on 11 December 2117, more than 105 years later. For most people alive today, the 2012 transit was therefore the first and the last one they could see. Move the orbit view to 6 June 2012 and the Sun, Venus and Earth are shown lined up in a row.
Viewing guide — where, when, how
Move the orbit view to 6 June 2012, follow Earth and set the Sun as the target to look at, and Venus is shown sitting exactly between Earth and the Sun. Move to 8 June 2004 and compare the two, and it becomes clear that the transits form a pair eight years apart.
Select Venus in the sky view for its position and shape (its phase) as seen from your location. Move the time to the morning of 6 June 2012 and Venus is drawn on top of the Sun's disk; speed up the playback to watch its crossing of more than six hours in a short time.
The next transit of Venus is in 2117. Before that there is a transit of Mercury on 13 November 2032. Mercury is smaller and farther away than Venus, so its dot on the Sun is much smaller, and a telescope with a solar filter is needed to see it.
See this for yourself — replay the moment in the orbit view
Why this eclipse is special
A transit of Venus is a practice problem for exoplanet science. When a planet passes in front of a star, part of the starlight shines through the planet's atmosphere, and the gases there absorb small amounts of certain colours. Reading those traces tells which gases the atmosphere contains. The atmosphere of Venus is already well known, so it made a good test of whether the method works.
The same idea later produced a major result. In 2022 the James Webb Space Telescope analysed the light of the exoplanet WASP-39b as it crossed its star and found carbon dioxide in its atmosphere. The 2012 observations of Venus were a valuable experiment, carried out inside the solar system, on the way to research like this.
The event has historical meaning too. In the 18th century Captain James Cook's expedition observed the 1769 transit of Venus from Tahiti. By comparing the times at which Venus touched and left the Sun's edge from different places, astronomers could work out the distance between Earth and the Sun. In 2012 the same sight was watched by space telescopes, satellites and a great many ordinary people.
Background and earlier eclipses
Transits of Venus are rare because the orbit of Venus is tilted slightly compared with Earth's. Venus passes between Earth and the Sun about every year and seven months, but usually it slips above or below the Sun. The places where the two orbits cross lie in the directions Earth faces in June and December, so transits happen only in those two months. The 2004 and 2012 transits were a June pair; 2117 and 2125 will be a December pair.
Different regions saw different parts of the 2012 transit. The beginning was seen from the Americas on the evening of 5 June, and the end from Europe, the Middle East and South Asia on the morning of 6 June. Most of South America and western Africa saw none of it. The whole event, from start to finish, was visible from north-east Asia including Korea and Japan, the Philippines, eastern Australia, New Zealand, the western Pacific, and far-northern places where the Sun does not set in June.
That made East Asia a good place to watch. In 2004 the Sun had set there before the transit ended, but in 2012 the entire transit fell in daytime. Observatories and science centres across the region held solar-viewing events. On the same day, aboard the International Space Station, astronaut Don Pettit photographed the transit through a solar filter he had brought along for it.
FAQ
Where could the whole transit be seen?
From north-east Asia including Japan, the Philippines, eastern Australia, New Zealand, the western Pacific and the high Arctic. There it fell entirely in daylight, from 22:09 UT on 5 June to 04:49 UT on 6 June 2012.
Why did it matter for exoplanet research?
Studying sunlight that passed through the atmosphere of Venus let astronomers test, inside the solar system, the method used to read the atmospheres of exoplanets crossing their stars.
When is the next one?
On 11 December 2117, followed by 8 December 2125.
How long did the transit last?
6 hours 40 minutes. Venus appeared about one thirtieth of the Sun's diameter, so it could be seen without a telescope through a solar filter.
Related
- Transit of Venus (2004)
- Transit of Mercury (2032)
- Venera 7 — landing on Venus
- Venus — object index
- The Sun — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.